Combination switch



Sept. 7, 1943. D. G. TAYLOR COMBINATION SWITCH Filed Feb. 19, 1941 3 Sheets-Sheet 1 :0 25 t2. m E N 0m 0 omu o0. 00 A 05 68 ozFfi: m. mutton muhz E m. cow 6 oo 8 3 H2024. uwz zu 55L 2 O r INVENTOR Do-rial G.Ta. lor- BY ATTORNEY p 7, 1943- D. 's. TAYLOR 2,329,094

COMBINATION SWITCH Filed Feb. 19, 1941 5 Sheets-Sheet 2 I IIIIII'II'IIIA 'Illllll- INVENTOR Daniel G. Tcv loy'- ya /aw ATTORN EY Sept. 7, 1943. G, TAYLOR 2,329,094

COMBINATION SWITCH Filed Feb. 19, 1941 s Shets-Sheet s INVENTOR Daniel G. Taslox ATTORNEY Patented Sept. 7, 1943 UNITED STATES PATENT OFFICE COMBINATION SWITCH Daniel G. Taylor, Minneapolis, Mimn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application February 19, 1941, Serial No. 379,566

18 Claims.

This invention relates to'automatic switching mechanisms, and one of its objects is to improve that type of mechanism wherein a plurality of switches are sequentially operated by'a single condition-responsive element; such as, for example, a combination fan and high limit control actuated by a temperature responsive element.

Another object of this invention is to provide improved means for adjusting the values of the controlling condition at which the switches are actuated.

Another object of this invention is to provide an improved strain release connection between a condition-responsive element and a switch, whereby overrun of the element will not produce undue strain on the parts of the mechanism.

A further object of this invention is to construct a mechanism for operating by means of a thermostatic element, a snap-action switch of the self-return type having a fixed differential between the force required to actuate the switch to one position and the force required to hold the switch in that position. A still further object is to provide, in such a device, means to reduce the differential between the temperatures at which the switch is operated to its two positions below the temperature differential normally required by the thermal element to produce the force and motion needed to operate the switch. A still further object of this invention is to construct such a device in which the diiferential between the temperatures at which the switch is operated to its two positions may be varied at will, within predetermined limits,

A further object of this invention is to construct a combined fan and limit control operated by a thermostat, and having means for adjusting the switch operating temperatures, in which. interlocking means is provided so that the fan control operating temperature may not be set higher than the limit control operating temperature.

A further object of this invention is to construct a combination control having a plurality of switches operable by a condition-responsiveelement, wherein a manual actuator is provided for simultaneously operating two of said switches independently of said element.

A further object is to provide, in a device having a plurality of switches operable by a condition-responsive element, improved means for calibrating the switches.

It has been proposed to use a mechanism such as that disclosed herein to control a hot air heating system provided with a fan to force the circulation of heated air through the house. In such a case the actuating thermostat for the control is placed in the bonnet of the furnace. The high limit switch is wired in series with the main controlling thermostat so as to shut down the 1 30 temperatures readily adjustable.

heating system in case the temperature of the air in the furnace bonnet becomes excessive. One or more switches are provided to control the operation of the fan, depending upon the num 5 ber of speeds at which the fan may be driven.

There is disclosed herein a two-speed fan control system, having one switch controlling the energization of the fan and a second switch controlling the speed at which it is driven. These switches are usually arranged to keep the fan deenergized when the air in the furnace bonnet is cool. As soon as the air in the furnace becomes warm enough to heat the house, the main fan switch closes to start the fan in operation. At this time, the speed changing switch is normally in such a position that the fan will operate at low speed. If the temperature continues to rise, the speed-changing switch operates and the fan changes to high speed operation. If the temperature then decreases, for any reason, the thermostatic element, at a certain predetermined temperature, operates the speed changing switch so as to run the fan at a lower speed. At a lower predetermined temperature, the main fan switch opens, and the fan is shut off.

It has been found desirable, in order to provide a device which i readily adaptable to suit the requirements of different heating systems, to make the main fan switch closing and opening It is also desirable to make the temperature at which the fan speed is changed and the temperature at which the limit switch opens adjustable. The operat ing diilerential of the speed-changing and limit switches, however, may be set at the factory at an optimum value with no inconvenience.

Since, in a device of this sort, the operating force supplied by the thermostatic element is small, it is essential that switches be used which may be operated with a minimum amount of force. I prefer to use switches of the self-return type such as that disclosed in the application of Albert E. Baak Ser. No. 307,991, filed December '7, 1939. It should be understood, however, that other switches of equivalent types may be used with the present device.

These and other objects of the present invention will readily become apparent as the following description is read in the light of the accompanying drawings, in which;

Figure 1 represents a front elevation of a combination fan and limit switch embodying my invention, with the cover removed,

Figure 2 represents a cross-section taken alone the lines 2--2 in Figure 1, looking in the direction of the arrows,

Figure 3 represents a view taken along the lines 33 of Figure 2, looking in the direction of the arrows,

Figure 4 is a plan view taken along the lines 4--4 in Figure 3, looking in the direction of the arrows,

Figure 5 is a detail view of a manually operable cam mechanism for actuating two of the switches of my control device,

Figure 6 is a plan view, on an enlarged scale. of the strain release connection used in my device,

Figure '1 is an elevation taken along the lines 1--1 of Figure 6, and

Figure 8 is an elevation taken along the lines 8-8 of Figure 6.

In the drawings is shown a casing l5 adapted to be mounted on the bonnet of a furnace, and having a shaft mounted on the back of the casing l so as to project into the interior of the furnace bonnet. A helical thermostatic element l2, of conventional type, is attached at one end to a collar 8 extending through the back of the casing I0 and fixed to a plate l3 inside the casing. The thermostatic element l2 surrounds the shaft I i, and the extreme end of the element l2 inside the furnace is attached to the end of the shaft The construction is such that a change in temperature in the furnace causes a rotation ofthe shaft H by the thermostatic element 2. The plate I3 is mounted so as to be adjustable about the axis of the shaft H, and its adjustment may be fixed by a bolt l4 which passes through an arcuate slot l in the plate IS.

The shaft terminates inside the casing 10 in an enlarged hub portion I6, which carries an L shaped crank arm l1. Mounted on the crank arm I1 is a two-way strain release mechanism generally indicated at and two one-way strain release mechanisms generally indicated at 2| and 22.

Supported in any suitable manner at the upper part of the casing I0 is a bracket plate 23 which carries means for adjusting the operating temperatures of the various switches. Mounted in the lower part of the casing III is a second bracket plate 24 which supports the switches themselves. The switch numbered 25 in the drawings is the main fan controlling switch while the switch numbered 25 is the speed changing switch for the fan. The limit switch is indicated a 21.

An insulating plate 28 is provided between switches 26 and 21. The limit switch is usually in a low voltage (e. g., 24 volt) control circuit, while the main fan and speed-changing switches are in a relatively high voltage (e. g., 110 volt) power circuit. The plate 28 guards against accidental connection of the two circuits. 0! course, both circuits may be operated at the same voltage, if desired.

The switch 25 is operated by moving an actuating button 30 which projects from the back of the switch casing through the bracket plate 24. The switch 25 is internally biased so that the button 30 normally extends backwards to a greater distance than that shown in Figure 2. Similar actuating buttons 3| and 32 extend backwardly from the switches 26 and 21 respectively. The buttons 30, 3| and 32 may be depressed to actuate their respective switches by means of levers 33, 34 and 35 respectively. These levers are mounted pivotally near the top of the back of the bracket plate 24 and each has an arm projecting forwardly above the top of the plate 24. These arms are numbered 40, 4| and 42 respectively in the drawings. The forward extremity of each f0 these arms is shaped so as to engage one end of a connecting link, These connecting links are numbered 45, 44 and 45 in the drawings, and their upper ends are operatively attached to the strain release connections 20, 2| and 22, respectively.

' The two-way strain release mechanism 25, shown in detail in Figs. 6 and 7, contains a driving member 50 which is mounted at one end on the crank arm H by any suitable means such as the bolt and nut shown at 49. The other end of the driving member 50 extends over the end of the axis of the shaft II, and has mounted thereon in line with the axis of the shaft H a hub member 55. Freely mounted for rotation about the hub member 55 are a link 5| and a link 52 separated by a spacing washer 55. Link 52 is rigidly connected to washer 55, so as to increase the length of the bearing surface of link 52 on hub 55. Washer 55 is provided with a shoulder 58 at its rear end on which a link 5| is pivoted. The purpose of the shoulder 55 is to bear against member 50 and prevent link 5| from being pinched by side thrust between washer 55 and member 50. The link 52 extends in a direction generally parallel to the driving member 55, and has mounted at its extremity nearest the crank arm H a hub member 51, on which is pivotally mounted an elongated link 53 which extends to the right of the other parts of the strain release mechanism 25 for a purpose to be described later.

On the driving member 50 at a point adjacent the crank arm 11 is an extension 50. One end of a tension spring 5| engages this extension 50 and the other end of the tension spring 5| engages a similar extension 52 projecting from the elongated link 53. Pivotally attached to the link 53 at a point in line with the axis of the shaft II is the upper end of the connecting link 43 which transmits the actuating force passing from the thermostatic element through the strain release 20 to the switch 25. It will be seen that the internal tension of the switch 25 acting through the lever 33, tends to move the link 45 downwardly and rotate the link 53 in a clockwise direction about the hub 51, The tension of the spring 5|, on the other hand, tends to rotate the link 53 about the hub 51 in a, counter-clockwise direction, and so opposes the effect of the internal spring in the switch 25.

The switch 25 used herein, as explained in detail in the Baak application Serial No. 307,991, previously referred to. The switch 25 has an enlarged portion 30a on the plunger 30 which cooperates with a raised portion of an actuating arm 25a. The arm 25a is of resilient material and is pivoted at 25b. A contact carrying rocker member 25c is pivoted on the central terminal post at 25d and is rocked thereabout by the arm 250. Sets of cooperating contacts 25c, 25,, 251, and 259, arecarried upon a resilient contact blade 257' which is suitably secured to the rocking member 250. A toggle member 25k abuts the lower end of the rocker member 250 and is biased into engagement therewith by a biasing spring 25m. The angle between the points of contact of the member 25k with the spring 25m and the rocker member 250 does not pass over center with respect to the pivot point 25d. With such structure, a spring rate compensation snap action is obtained.

The operation of the switch 25 is as follows: When the button 30a is moved to the left, tension is stored in the resilient member 25a. This tension is resisted by the spring 25m which acts upon the toggle member 251:. This toggle member engages the rocker member 250 at an angle. This angle and the tension in the spring m are so selected that they will resist the tension in the resilient member 25a to a predetermined extent. However, when the tension of member 25a overcomes the tension of spring 25m the member 25a begins to move toward the left, this resisting force will decrease at a rate more rapid than the decrease of force exerted by the member 2511. Because of this change in force relationship, the contacts will be snap actuated with what is termed a spring rate compensation snap action. In this type of action the tendency of the contacts to move together increases as they approach each other. This function could also be obtained by a magnetic snap action of the self return type in which the contacts are attracted together with a greater magnetic force as the contacts are brought more closely together. It is to be understood that other types of switches having a similar characteristic could also be substituted for the switch 25 without interfering with the operation of the present control device.

The switch 25 requires a certain force to hold the button in its inward position (as in Fig. 2), and a greater force to move the button 30 from its outward position to its inward position. The spring 6| is chosen so that its tension is inter mediate the values of these two forces. Therefore, when the button 30 is in its inward position, spring 6| exerts a force greater than the minimum required to hold the button in, so that it remains in that position. On the other hand, when the button 30 is in its outward position,

the force exerted by spring BI is not sufiicient to overcome the internal tension of the switch 25. The switch therefore tends to remain in whichever position it may be, until some external force other than that of spring 6| is exerted upon the button 30.

The link 5|, which is pivotally mounted on the hub adjacent driving member 50, has a projection 63 extending rearwardly therefrom which serves to engage the driving member 50 and thereby limit the counter-clockwise rotation of the link 5| with respect to the driving member 50. The link 5! also has a downwardly extending projection 64 which carries one end of a tension spring 65. The other end of the tension spring engages a downwardly extending projection 66 on the link 52. The link 52 also has a. rearwardly extending projection 61 (see Fig. 6) which engages a portion of the link 5| so as to limit the clockwise rotation of link 52 with respect to link 5|. It will be seen therefore that the spring 65 tends to hold the stop 61 in engagement with the link 5|,

It should be noted that the tension of spring 6| also tends to rotate the link 53 about the end of link 43 as a fulcrum, and therefore exerts a counter-clockwise torque on the hub 51. This torque is transmitted through the link 52 and spring 65 to .link 5|, and thus tends to hold extension 63 against driving member 50.

The one way strain release mechanism 2|, which is shown in detail in Figures 6 and 8, has a driving member 10 which is attached to the crank arm I 'l by means of a bolt 1|. Pivotally attached to the driving member 10 at a point in line with the axis of the shaft H is a link 12. On the driving member 10 is a projection 13 to which is attached one end of a tension spring 14. The other end of the tension spring 14 is attached to a similar projection 15 on the link 12. On the link 10 is another projection 16 through a portion of which is threaded a bolt 11 so as to engage a. similar projection 18 on the link 12. It will be seen that the tension of spring '14 tends to rotate the link 12 in a counterclockwise direction about the pivot on the driving member 10 but that its counterclockwise rotation is limited by the engagement of the bolt 11 with the projection I8. Pivotally mounted on the link 12 at a point 18 spaced from the axis of rotation of the shaft H is another link 80, which has one end extending to the right of the other parts of the strain release mechanism 2| and its other end overlying the end of the axis of the shaft ll. Attached to the link at this end is the connecting link 44 which transmits motion passing from the thermostatic element through the strain release mechanism 2| to the speed changing switch 26.

The one-way strain release mechanism 22 is similar in detail to the strain release mechanism 2| and will not be described further.

Pivotally mounted on the back of the plate 23, are a plurality of adjusting members 8|, 82, 83 and 84. These adjusting members are provided with forwardly extending projections numbered 85, 86, 88 and 81 respectively. The projections 85 and 86 extend through a slot 90 at the right hand side of the plate 23 and indicate on the scale adjacent that slot the temperatures at which the main fan switch will be actuated to its off and on positions, respectively, in a manner to be described later, The projections 81 and 88 extend through a similar slot 9| on the left hand side of the plate 23 and indicate on a scale adjacent that slot the temperatures at which the limit switch and speed change switch, respectively, will be actuated. These adjusting members 8|, 82, 83 and 84 also have rearwardly extending projections 92, 93, 9d and respectively, which project into the path of motion of the links 53, 80 and the link corresponding to 80 in the strain release mechanism 22. The member 64 is provided with a lug 96 which extends above the member 83 and prevents the limit switch from being adjusted at a lower temperature than the speed-changing switch. The member 83 is provided with a similar lug 91 which extends above the members 8| and 82 and prevents the main fan switch from being adjusted to turn on the fan at a higher temperature than that at which the speed is changed to high.

Means is provided for compensating the spring rate of the thermostatic element |2 so that it will not adversely aiiect the operation of the main fan switch 25. This means includes a stop member |0| which is mounted on the back of the bracket plate 24 and has a relatively narrow portion. The lever 33 is mounted so that a portion of it travels along this narrow portion and is limited in its motion in both directions by engagement with the enlarged portions. The lever 33 is provided at its lower extremity with a saddle I02 in which one end of a toggle link I03 is carried. The other end of the toggle link I03 is carried in a similar saddle I04 on a spring member I05 which is mounted for adjustment relative to the plate 24. The spring member I05 is attached to a flexible bracket I06. A bolt |0| passes through the bracket |06 so as to engage the back of the plate 24. By turning the bolt I07 the position of the bracket I06 and hence of the saddle I04 on the spring member I05 may be adjusted.

It is often desired, in heating systems having a fan for forcing circulation of air, to utilize the fan for cooling purposes during the summer, when the furnace is not in operation. Means have therefore been provided in the present device for manually closing the fan energizing circuit and simultaneously moving the speed controlling switch to high speed position. A shaft H is journaled in the bracket plate 23, and extends forwardly thereof. At its forward end is a knurled knob Ill, so that the shaft may be readily rotated by hand. Rigidly mounted on the shaft Hi! just inside the plate 23 is a cam member I I2, shown in detail in Fig. 5. A stop H3 mounted on the plate 23 cooperates with a pair of shoulders H4 on the cam 2 to limit rotation thereof in either direction. A spring member H5 mounted on theplate 23 cooperates with a pair of notches H8 on the cam to maintain it in either of the extreme positions to which it may be rotated. A spring arm Ill, mounted on the lever 33, projects into the path of a shoulder H8 of the cam H2. A similar spring arm H9, mounted on the lever 34, projects into the path of a shoulder I20 on the cam H2. A groove 12! on the outer end of the shaft H0 cooperates with suitable indicia on the plate 23 to show whether the manual actuating means is set for winter heating or summer cooling.

Operation The operation of the speed changing switch 26 through the one-way strain release connection 2| will first be described. Let it be assumed that the parts are in the position shown in the drawings and that the furnace temperature is relatively low. At this time the switch actuating button 3i is held in its outward position by the internal bias of the switch 26. The forwardly extending arm 4| of the lever 34 is therefore in its lowered P sition, and the link 44 is in a position such that its upper end is at a position such as shown in Figure 8. The connections of the bimetallic element l2 are such that an increase in temperature will cause the crank arm I! to be rotated in a counter-clockwise direction as viewed in Figure 8. Considering Figure 8, let it be assumed that the furnace temperature begin to rise with the result that the crank arm I! moves in a counter-clockwise direction about the axis of the shaft ll. When the furnace temperature reaches the value for which the indicating finger 88 of the adjusting plate 83 has been set, the right hand end of the link 80 as viewed in Figure 8, will engage the projecting arm 94 which is a part of the adjusting plate 83. When this occurs, further counter-clockwise rotation of the crank arm I! will cause the link 80 to turn about stop 94 as a fulcrum, and thus a lifting force will be applied to the upper end of the link 44. This force will be transmitted through link 44 and extension 4| of lever 34 and will oppose the internal bias of the switch 26. As the temperature continues to rise, this force will become sufficient to overcome the internal bias and will cause the lever 34 to move the switch actuating button 3i inwardly thus moving the speed changing switch 26 from its low speed to its high speed position. When the button 3| has reached the limit of its inward movement further upward movement of the link 44 will be prevented. The link 80 will therefore be held at both its ends. Further increase in the furnace temperature will cause the bolt T! to separate from the projection 18 and will cause an increase in the tension of spring 14. It may therefore be seen that an increase in the temperature of the furnace beyond that at which the speed changing switch is set to be actuated will not place any undue strain on either the bimetallic element or the switch but will merely cause an increase in tension or stretching of the spring I4.

Let it now be assumed that the temperature in the furnace decrease from the relatively high value attained. This will move the crank arm I! in a clockwise direction. As soon as the bolt 11 engages the projection 19, the driving member Hi and the link 12 will move clockwise together and the internal bias of the switch 26 will become effective to move the left end of link 44 downwardly, rotating the link 90 about the pivot 19 until the switch has reached its normal low peed position. Further counter-clockwise movement of the crank arm I! will merely cause the link to pivot about the upper end of the link 44 which is in line with the axis of the shaft H.

Upward movement of link 44 is limited by the button 3! reaching its innermost position, while its downward movement is limited by the engagement of lever 4| with the bottom of plate 23. The parts are so proportioned that the total movement of link 44 is relatively small, and its upper end is always substantially in line with the axis of rotation of shaft II.

The operation of the limit switch 21 is the same as that of the speed changing switch Just described. In the case of the limit switch, the stop 95 on the adjusting plate 84 cooperates with the strain release connection 22 to determine th temperature at which the limit switch will be actuated.

, The operation of the main fan switch 25 will now be described. Let it be assumed that the furnace temperature is below that at which the indicator 85 has been set to turn the fan switch off. The various parts will then be in the position shown in the drawings. It should be noted that the switch actuating button 30 has been pressed inwardly from the position to which it is biased by the internal spring of the switch 25. It should also be noted that the extension 40 on the lever 33 has been lifted from its normal position, and that the link 53 has been moved against the stop 92. The internal bias of the switch 25 acts, through the lever 33, downwardly on the link 43, tending to turn the link 53 in a clockwise directionabout the pivot 51. This tendency is opposed by the tension of the switch spring 6| which tends to move the link 53 in a counterclockwise direction about the pivot 51. This spring II is chosen so that its tension matches that of the internal bias of the switch 25. The resultant of these two tensions is therefore substantially zero.

Let it now be assumed that the temperature in the furnace begins to rise with a consequent counter-clockwise rotation of the crank arm I! about the axis of shaft I I. This movement of the crank arm I! will carry the driving member 50 with it, and the motion will be transmitted through the spring BI and link 53 to the links 52 and 5|. The whole strain release assembly shown in Figure 7, with the exception of the link 43 and the stops 92 and 93, will therefore tend to turn in a counter-clockwise direction about the axis of the shaft II. This action will continue until the link 53 engages the stop 93. When this occurs further increase in temperature in the furnace will cause the link 53 to be pivoted counter-clockwise about the stop 93 as a fulcrum, thus moving the link 43 downwardly. The tension of the spring 9| will then be opposed by the stop 93, and the internal bias of the switch 25 will move the switch actuating button 30 outwardly, thereby completing the energizing circuit of the fan and starting the fan in operation. If the furnace temperature continues to rise after the link 43 has reached its downward limit of movement, the link 53 will remain stationary since it is held by link 43 and stop 93, and the only effect will be stretching of the spring 6|. The link 5| will be held stationary as the pivot 51 cannot move. The extension 61 will prevent counter-clockwise rotation of link 5| with respect to link 52. Therefore, link 5| will also remain stationary, and the stop member 53 will separate from the driving member 50.

If the furnace temperature now begins to decrease, the crank arm I 1 will be moved in a clockwise direction. Until the driving member 50 engages the projection 63, the only effect of this motion will be to decrease the stretching of the spring 6|. As soon as the driving member 50 engages the projection 63, the link 5| is also driven clockwise and a force is transmitted through the spring 65 to turn the link 52 clockwise about the pivot 55. This moves the pivot 51 and hence the link 53 in a clockwise direction. All the links 5|, 52 and 53 are then moving together. Since the tension of the spring 5| balances that of the internal bias of the switch 25, no movement of the link 43 takes place, however, until the right hand end of link 53 engages the stop 92. Therefore the fan controlling switch 25 continues to keep the fan circuit closed until a temperature is reached which has been determined by setting the stop 92 through the movement of the indicator 85 adjacent the scale on the bracket plate 23. When this temperature is reached, further clockwise rotation of the link 53 about the axis of the shaft H is prevented by the engagement of its right hand end with the stop member 92. As the crank arm I! and the pivot 51 continue to move clockwise the link 53 is pivoted about the stop 92 as a fulcrum, transmitting a lifting force to the end of the link 43. The resulting upward movement of the link 43. causes the lever 33 to press inwardly on the actuating button 30 and move the switch 25 to its off position.

If the temperature in the furnace continues to fall until the link 43 reaches its upper limit of movement as determined by stop then the link 53 is held from further movement. Since the motion of the pivot 51 is stopped, the link 53 is also prevented from further counterclockwise rotation. The link continues to be driven counterclockwise by the engagement of the projection 53 with the driving member 50. Stop 61 separates from link 5|, and strain on the parts of the mechanism is prevented, by the stretching "of the spring 65 to take up any additional motion of the crank arm i1.

It should be clear from the preceding description that I have provided a strain release connection which prevents strain on the mechanism after the driven member has been prevented from further movement in either direction. It should be noted that the link 43 is biased in a downward direction, and that the spring 8| has a dual function, first to oppose the bias of the link 43 so that the link 53 will remain in any position to which it is moved, and second to act as a strain release spring when the counterclockwise rotation of the link 53 has been stopped and the crank arm I! is continuing to rotate in that direction.

Switches of the type disclosed in the description of the present instrument have a fixed differential between the force necessary to push the switch actuating button inwardly and the .force needed to hold the button in an inward position. The minimum temperature differential normally obtainable between the fan off and fan on temperatures with the stops 92 and 93 moved as close to each other as possible, would, therefore, be equal to the difierential between that temperature at which the helical thermostatic element |2 produces a force equal to the actuating force described and the temperature at which the thermostatic element produces a force equal to the holding force described plus the temperature differential required by the element l2 to move itself through the distance required for operation of the switch. It has been found, however, that the normal temperature diiferential thus obtained is too large to provide optimum operation of the present device, because in certain types of heating systems, it is necessary or desirable that the minimum temperature differential be adjustable to a value much smaller than this. The applicant has therefore provided means whereby the minimum temperature differential is reduced below this normal value. This means comprises the toggle link I03 and the spring I05, and its proximate function is to compensate the spring rate of the helical thermostatic element l2.

Consider the case of a flexible member, or spring, rigidly supported at one point and having a deflecting force applied at another point. For any given flexible member, a force of a certain magnitude will produce a certain deflection. An increase in the deflecting force will produce an increase in the deflection. The increment of the deflecting force, divided by the resulting increment of the deflection, is termed the spring rate of the member.

The helical thermostat element I2 is a flexible member which is so constructed that it spring rate is a constant.

The operation of this type of helical thermostatic element when subject to an external deflecting force is as follows. If the element is fixed at one end, and a deflecting force applied to its opposite end, the ambient temperature remaining constant, the deflection will be proportional to-the deflecting force, and the proportionality will be determined by the same constant spring rate as before. Similarly, if both ends of the element are fixed, and the temperature changes, a force will be exerted at both ends of the element which is proportional to the temperature change. If, after such a temperature change, one end is released, that end of the element will deflect to a new position corresponding to the new temperature, and the external force exerted by the element will gradually decrease to zero as the deflection takes place.

Operation of switch 25 without spring rate compensation Now consider the operation of the switch 25 by the element i2 as if the toggle link I03 and the spring I05 were absent. In order to simplify the present discussion, the action of the strain release mechanism maybe disregarded except as it serves to change rotation of the arm I! into translation of the link 43. Let it be assumed that the stops 92 and 93 are set to engage the opposite sides of the arm 53 simultaneously so that the device will operate with a minimum temperature differential between the on and off positions of the switch 25, and that the other parts are in the positions shown in the drawings. It should be remembered that the switch 25 is internally constructed so that the force required to move the button 30 inwardly (from right to left in Fig. 2) is greater than the force required to hold the button in its inward position. The minimum force required to move the button inwardly past the operating point of the switch will hereinafter be referred to as force M, and

the minimum force required to hold the button.

inwardly will be identified as force H. Obviously, M is greater than H with the switch button 30 in its inward position, as shown, the switch is open, and a force of a value between M and H is acting through the lever 33 to move link 43 downward. This force is opposed by an equal and opposite reactive force supplied by the element I2. The element I2 is therefore deflected from the normal position it would assume if left free to move. Now let the temperature begin to rise. The construction is such that a rise in temperature will cause the reactive force supplied by the element I2 to decrease below H and th link 43 will therefore move downwardly. As link 43 moves, the switch button 30 will be moved to its closed position, paralleling the change in the position of the element I2 as the temperature increases. The difference in temperature needed to move the switch button 30 from open to closed position is therefore the temperature differences needed to move the element I2 through a distance corresponding to the travel of the link 43. (As previously explained, the latter temperature difference is determined by the spring rate of the element I2.) Let this temperature difference be designated as T1.

After the switch has been moved to closed position because of an increase in temperature equal to T1, let it be assumed that the temperature begins to decrease. This decrease in temperature causes the element I2'to deflect so as to move link 43 upwards. The force needed to move link 43 upward is now M, greater than H. The upward reactive force applied to the link 43 by the element I2 is at this moment slightly less than H. The difference between this momentary value and H may be neglected for all present purposes. As the temperature decreases, this upward force increases proportionally, but no movement of the link 43 takes place until it reaches the value M. Let the temperature difference required to increase the upward force exerted by the element I2 from H to M be designated as T1.

After the force exerted by the element I2 has reached the value M, further decrease in temperature will cause the link 43 to move toward its upper position. The temperature difference necessary to complete this movement will be the same as that required for the downward movement, or T1. The differential between the temperatures at which the switch is actuated to on and oil positions is therefore equal to T1 plus T1.

Operation of suiitch 25 with spring rate compensation Now consider the operation of switch 25 by the element I2 when the toggle link I03 and spring I05 are present.

As in the previous case, assume that the button 30 is in its inward position, and that the force H is acting to move the link 43 downward. The spring I05, however, introduces a new force into the picture, having a component X, which opposes the force H. Therefore the upward reactive force which element I2 must supply in order to hold button 30 in its inward position is now only H minus X. Let the temperature now increase. This decreases the upward force supplied by element I2, and link-43 starts to move downward. As soon as the link 43 starts to move downward, the lower end of lever 33 starts to move to the right. This changes the angle at which the toggle link I02 acts on the lever 33, so as to reduce the component X which is effective to oppose force H. Although the change in the deflection of element l2 due to downward movement of link 43 causes an increase in the reactive force supplied by that element, the proportions of spring I05 and toggle link I02 are so chosen that the component X decreases faster than the reactive force increases, and hence the link 43 moves downward with a sudden snap. In other words, the rate of decrease of component X compensates for the rate of increase of the reactive force, which is governed by the spring rate of the element i2. This action is known and described by the term spring rate compensation.

After the toggle link I02 oes over center, the component of force due to spring I05 which acts on the push button 30 is no longer opposing force H, but aiding it, and the aid increases as the movement continues. This component which aids H will be referred to as force Y. The toggle mechanism may be adjusted so that the center position is at the center of travel of lever 33, and X is equal and opposite to Y. The toggle mechanism is so designed that X and Y are small compared with H, and also the deflection of element I2 corresponding to the force X, or Y, is small compared to the deflection corresponding to T1. The temperature increment necessary to secure a deflection corresponding to force X, or Y, will be designated as T3.

After the switch has been thus moved to closed position let it be assumed that the tem perature begins to decrease. The force needed to move the link 43 upward is now M plus Y. The reactive force of the element I2, having been equal to slightly less than (H minus X) at the start of the downward movement, and having been increased by an increment Y during that movement, is now slightly less than (H minus X plus Y). Since X equals Y, the reactive force is slightly less than H, just as it was at this stage of operation without the spring rate compensation. As before, the slight difference between this momentary value and H may be neglected. As the temperature decreases, this upward reactive force increases proportionally but no movement of the link 43 takes place until it reaches the value M plus Y. The temperature difference required to change the force exerted by the element I2 from H to M has been designated as T2, and the temperature increment required to secure the force Y has been designated as T3. When the link 43 starts to move upward, the force Y decreases due to the change in angle of the toggle link I03 faster than the reactive force decreases due to the spring rate of the element I2, and the switch 25 snaps to its open position with no further decrease in temperature.

Therefore the minimum temperature differential between open and closed positions of switch 25 is equal to (T1 plus Ta) when the spring rate of the element I2 is compensated by the action of toggle link I02 and spring I05. It was previously shown that the minimum temperature difierential when the spring rate was uncompensated was Tz plus T1. Since T3 is smaller than T1, as explained above, the differential has been decreased by compensating the spring rate of the element l2.

Sequence of operation If the knob III is set, as indicated in Figure 1, for winter operation, and the actuating temperatures of the various switches are adjusted by setting theindicators 85, 86, 81 and 88 at the positions shown in Figure 1, then with the furnace temperature below the lowest of these settings, the fan switch will be open, the speedchanging switch in low speed position, and the limit switch will be closed.

Assume that a fire-is started in the furnace under such conditions, as the temperature rises, the fan switch will be closed at approximately 130,

as shown by the indicator 86, and the fan will begin to run at low speed. If the temperature continues to rise to 150, the speed changing switch will be actuated and the fan will operate at high speed. If the temperature continues to rise to 230, the limit switch will beopened and on a temperature drop, due to the inherent differential of the switch.

If the knob III is moved from its winter position to its summer position, the cam H2 will be rotated counterclockwise from the position shown in Figure 5, and the shoulders I I8 and I will engage the arms Ill and H9. Engagement of arm ill by shoulder H8 will force the lever 33 downwardly, moving the main fan switch to on position. Engagement of the arm H9 by shoulder I20 will move the lever 34 upwardly, move the switch 26 to high speed position. The fan will then operate at high speed to circulate air through the house for cooling purposes.

Galibratz'on After the device has been assembled, the temperatures of the element l2 at which the fan switch 25 is actuated may not agree with those indicated on the scale adjacent the slot 90 by the fingers 85 and 86. The thermostatic element may be adjusted for calibration purposes by means of the bolt I4 and the adjustable plate i3. When the switch 25 has been calibrated in that manner, the speed-changing switch may be brought into calibration with its scale by means of the bolt 11, which changes the temperature at which the stop 94 is engaged by the link 30. A similar adjustment may be made in the strain release mechanism 22 associated with the limit switch 21.

Although I have described my invention in connection with a combined two-speed fan and limit control, other modifications will occur to those skilled in the art. For example, my device might be used with a single speed fan control, or low limit and overrun controls might be incorporated. My invention is to be limited, therefore, only by the scope of the appended claims.

I claim as my invention:

1. A condition responsive control device, comsaid spring means is rendered ineffective, and

prising in combination, an element movable in accordance with the magnitude of a variable con dition, a driving member connected to said element and rotatable about an axis upon movement thereof, control means operable between a first position and a second position, a driven member movable transversely to said axis and operatively connected to said control means, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link in each direc-' tion, and a two-way strain release between said driving member and said link, said strain release comprising a first flexible connection including spring means tending to rotate said link in a clockwise direction, and a second flexible connection including spring means tending to rotate said link in a counterclockwise direction, said spring means balancing each other so that said link rotates with said driving member until said stop means is engaged, whereupon one of said spring means is rendered ineffective, and the other spring means becomes effective to move said link transversely of said axis, thereby moving said driven member and operating said control means,

2. In a condition responsive control device, a driving memberrotatable about an axis in accordance with the magnitude of a variable condition, a driven member movable transversely to said axis between a first position and a second position, a first link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link about said point in each direction, and a strain release between said driving member and said link comprising a second link pivotally attached to said first link at a point spaced from said axis and rotatably attached to a fixed pivot in line with said axis, a third link rotatably attached to said fixed pivot, a portion of said second link adapted to engage a portion of said third link so as to limit relative rotation between said links in one direction, spring means connecting said links and biasing said portions into engagement, a. portion of said third link adapted to engage a portion of said member so as to limit relative rotation therebetween in the opposite direction, and spring means connecting said first link and said member and acting through said second and third links to bias said last-mentioned portions into engagement.

3. In a condition responsive control device, a driving member rotatable about an axis in accordance with the magnitude of a variable condition, a driven member movable transversely to said axis between a first position and a second position, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link about saidpoint in each direction, and a strain release between said driving member and said link comprising a first flexible connection including spring means tending to rotate said link in a clockwise direction and a second flexible connection including spring means tending to rotate said link in a counterclockwise direction, said spring means balancing each other so that said link rotates with said driving member until said stop means is engaged, whereupon one of the other spring means becomes effective to move said link transversely of said axis, thereby operating said driven member.

4. In a condition responsive control device, a

driving member rotatable about an axis in accordance with the magnitude of a variable condition, a driven member movable transversely to said axis between a first position and a second position, means biasing said driven member to said first position, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link about said point in each direction, and a strain release between said driving member and said link comprising a first flexible connection including spring means tending to rotate said link in a clockwise direction and a second flexible connection including spring means tending to rotate said link in a counterclockwise direction, one of said spring means balancing the other spring means and said biasing means so that said link rotates with said driving member until said stop means is engaged whereupon one of said spring means is rendered inefiective, and the link is moved transversely of the axis under the influence of the other spring means and the biasing means, so as to operate said driven member.

5. A condition responsive control device, comprising in combination, an element movable in response to a variable condition, a pair of control devices, a housing for supporting said element and said devices, connections between said element and each of said devices, said housing having a pair of slots therein and a scale adjacent each slot, said connections comprising, for each said device, an adjustable member having a finger extending through one of said slots,

means whereby the position of each said member determines the value of the condition at which the corresponding control device is actuated, and whereby each said finger indicates said value on the adjacent scale, and means for interlocking said member so that the actuating value determined by one finger is always lower than that dtermined by the other.

6. A condition responsive control device, comprising in combination, an element movable in response to a variable condition, a pair of control devices, a housing for supporting said element and said devices, connections between said element and each of said devices, a manual operator mounted so as to extend into said housing,

connections between said operator and each of said devices so that both devices may be actuated simultaneously by manipulation of said operator, regardless of the position of said movable element.

7. In a condition responsive control device, a driving member rotatable about an axis in accordance with the magnitude of a variable condition, a driven member movable transversely to said axis between a first position and a second position, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link about said point, and a strain release between said driving member and said link comprising a second link pivotally attached to said first link at a point spaced from said axis and rotatably attached to a pivot on said driving member in line with said axis, spring means tending to rotate said second link relative to said driving member, and means for limiting the rotative tendency of said spring means.

8. In a condition responsive control device, a driving member rotatable about an axis in accordance with the magnitude 01' a variable condition, a driven member movable transversely to said axis between a first position and a second position, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link about said point, and a strain release between said driving member and said link comprising a second link pivotally attached to said first link at a point spaced from said axis and rotatably attached to a pivot on said driving member in line with said axis, spring means connected to said driving member and to said second link and tending to rotate said second link relative to said driving member, and stop means on said driving member for limiting said rotative tendency.

9. In a condition responsive control device, a driving member rotatable about an axis in accordance with the magnitude of a variable condition, a driven member movable transversely to said axis between a first position and a second position, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link about said point, and a strain release between said driving member and said link comprising a second link pivotally attached to said first link at a point spaced from said axis and rotatably attached to a pivot on said driving member in line with said axis, spring means connected to said driving member and to said second link and tending to rotate said second link relative to said driving member, and adjustable stop means on said driving member for limiting said rotative tendency, and for determining the relative normal positions of said member and said second link.

10. A condition responsive control device, comprising in combination, a flexible element movable in response to a variable condition, control means biased to a first position and having a fixed differential between the force required to move said means to a second position and the force required to hold said means in said second position, means operatively connecting said element with .said control means, and a device to compensate the spring rate of said element.

11. A condition responsive control device, comprising in combination, a flexible element movable in response to a variable condition, control means biased to a first position and having a fixed differential between the force required to move said means to a second position and the force required to hold said means in said second position, mean operatively connecting said element with said control means, a device to compensate the spring rate of said element, and a strain release to prevent strain of the parts due to overrun of said element after actuation of said control means.

12. A condition responsive control device, comprising in combination, a flexible element movable in response to a variable condition, control means biased to a first position and having a fixed diflerential between the force required to move said means to a second position and the force required to hold said means in said second position, means operatively connecting said element with said control means, a device to compensate the spring rate of said element, and means for independently varying the values of said condition at which each of said forces is transmitted to said control means.

13. In a condition responsive control device, a. condition responsive driving member movable in accordance with the magnitude 01 a variable condition, a driven member movable between a first position and a second position, means independent of said condition responsive driving member for biasing the driven member to said first position, a strain release mechanism operatively connecting said members and including spring means, said spring means acting on said driven member in a direction opposite to that of said independent biasing means.

' 14. In a condition responsive control device, a driving member movable in accordance with the magnitude of a variable condition, a driven member movable between a first position and a second position, means independent of said driving member for biasing the driven member to said first position, spring means connected between said driven member and said driving member, said spring means operatively connecting said members and opposing said independent biasing means so that said driven member remain in either of said positions to which it is moved by said driving member.

15. A condition responsive control device, comprising in combination, an element movable in accordance with the magnitude of a variable condition, a driving member connected to said element and rotatable about an axis upon movement thereof, control means operable between a first position and a second position, a driven member movable transversely to said axis and operatively connected to said control means, a link pivotally attached to said driven member at a point substantially in line with said axis, stop means for limiting the rotation of said link in each direction, a two-way strain release between said driving member and said link, said strain release comprising a first flexible connection including spring means tending to rotate said link in a clockwise direction, and a second flexible connection including spring means tending to rotate said link in a counterclockwise direction, said spring means balancing each other so that said link rotates with said driving member until said stop means is engaged, whereupon one of said spring means is rendered ineffective, and the other spring means becomes efiective to move said link transversely of said axis, thereby moving said driven member and operating said control means, and manual means for actuating said control means regardless of the position of said element.

16. In a condition responsive control device, a driving member movable in accordance with the magnitude of a variable condition, a driven member movable between a first position and a second position, first spring means for biasing the driven member to said first position and opposing movement of said driven member to said second position in response to said driving member, second spring means opposing said first spring means and operatively connecting said driving member to said driven member for movement of said driven member to said first position, and third spring means opposing said first spring means and operatively connecting said driving member to said driven member for movement of said driven member to said second position.

1'7. In a condition responsive control device, a condition responsive driving member movable in accordance with the magnitude of a variable condition, a driven member movable between a first position and a second position, first spring means opposing independent movement of said driven member to the first position and operatively connecting said driving member to said driven member for movement of said driven member to said first position, and second spring means opposing independent movement of said driven member to the first position and operatively connecting said driving member to said driven member for movement of said driven member to said second position.

18. A condition responsive control device, comprising in combination, a flexible element movable in response to a variable condition, control means biased to a first position and having a fixed differential between the force required to move said means to a second position and the force required to hold said means in said second position, means operatively connecting said element with said control means, and a snap action spring member acting upon said connecting means in such a manner as to compensate the spring rate of said element.

DANIEL G. TAYLOR. 

